Conventionally, there was a technology of intending to reduce a noise added to a preamplifier output signal when a preamplifier input signal changes from a small level signal to a large level signal as a preamplifying circuit (for example, see JP-A-2001-320253).
In addition, conventionally, there was a technology of making a voltage standing wave ratio at input and output terminals excellent and intending to set an attenuation of gain arbitrarily regardless of existence of gain variability, as a gain controllable amplifier (for example, see JP-A-2004-194105).
Moreover, conventionally, there was a technology of performing AGC (Automatic Gain Control) of both a preamplifier and a postamplifier, as an optical receiving circuit (for example, see JP-A-2003-318681, JP-A-Hei11(1999)-266126, and JP-A-Hei2(1990)-278906).
Moreover, conventionally, there was a technology of performing AGC of a preamplifier by binary control and hysteresis control, as an optical receiving circuit (for example, see JP-A-2006-262003).